Psoriasis is a skin disease characterized by a hyperproliferation of keratinocytes and a disorder in their differentiation.
An inflammation of the dermis also arises, with vascular and immunological changes involving an activation of T lymphocytes.
This hereditary disorder, benign in the great majority of cases, manifests itself in more or less extensive erythemato-squamous plaques on the cutaneous integument, causing sometimes great suffering for the patient and for those around the patient.
Though often localized at the elbows and forearms, on the knees and legs, and in the lumbar and gluteal region, the lesions can extend to the rest of the body.
Sometimes, on account of its great extent, amounting to a psoriasis universalis or even an erythrodermic psoriasis, due to its particular pustular form or to its association with arthritis, psoriasis amounts to a very grave and crippling disease that may place a patient's vital or functional prognosis at risk.
The treatment of psoriasis by the oral administration of 5-methoxypsoralen in doses between 1 mg and 1.2 mg per kilogram of body weight, by a session of PUVA therapy, and further ultraviolet irradiation, has been covered by French Patent 2,406,444.
On account of the difficulties involved in prolonged general PUVA treatments it is particularly important to be able to have a local treatment on a body area exposed to reduced ultraviolet radiation.
The present invention has precisely the purpose of providing a composition making it possible to avoid certain problems involved in oral treatment, and to proceed in particular with a topical treatment of psoriasis of limited extent or of stubborn plaques, which have subsisted after oral treatment.
The present invention has as its subject matter a pharmaceutical composition intended for topical application, characterized in that it comprises 5-methoxypsoralen (5-MOP) in a concentration of 60 ppm to 100 ppm, and more particularly of 65 ppm to 95 ppm, in a pharmacologically acceptable oleaginous formula.
Compositions particularly preferred in the scope of the present invention include 5-MOP in a concentration of the order of 75 ppm.
Natural essences of citrus, such as the essence of natural bergamot, which contains 5-methoxypsoralen, are generally used.
The pharmaceutical compositions of the invention also include one or more ultraviolet B ray filters, selected from among ethyl-hexyl paramethoxycinnamate, trimethylbenzylidene heptanone, etc.
The compositions of the invention are presented in an oily excipient or in the form of continuous-phase lipidic emulsions.